University of Tunis El Manar, Faculty of Sciences of Tunis Laboratory of Materials, Crystal Chemistry and Applied Thermodynamics, El Manar II, Tunis 2092, Tunisia.
University of Cologne, Faculty of Mathematics and Natural Sciences, Department of Chemistry, Institute for Inorganic Chemistry, Greinstrasse 6, D-50939 Köln, Germany.
Molecules. 2023 Jan 11;28(2):731. doi: 10.3390/molecules28020731.
Two isomeric 2-bromomethylpyridine Cu(II) complexes [Cu(CHNBr)(NO)] with 2-bromo-5-methylpyridine (L) and 2-bromo-4-methylpyridine (L) were synthesized as air-stable blue materials in good yields. The crystal structures were different with [Cu(L)(NO)] () crystallizing in the monoclinic space group 2/c, while the 4-methyl derivative was solved and refined in triclinic 1¯. The orientation of the Br substituents in the molecular structure ( () vs. () conformations) and the geometry around Cu(II) in an overall 4 + 2 distorted coordination was very different with two secondary (axially elongated) Cu-O bonds on each side of the CuNO basal plane in or both on one side in . The two Br substituents in come quite close to the Cu(II) centers and to each other (Br⋯Br ~3.7 Å). Regardless of these differences, the thermal behavior (TG/DTA) of both materials is very similar with decomposition starting at around 160 °C and CuO as the final product. In contrast to this, FT-IR and Raman frequencies are markedly different for the two isomers and the UV-vis absorption spectra in solution show marked differences in the π-π* absorptions at 263 () or 270 () nm and in the ligand-to-metal charge transfer bands at around 320 nm which are pronounced for with the higher symmetry at the Cu(II) center, but very weak for . The -dependent susceptibility measurements also show very similar results ( = 1.98 µ for and 2.00 µ for and very small Curie-Weiss constants of about -1. The EPR spectra of both complexes show axial symmetry, very similar averaged values of 2.123 and 2.125, respectively, and no hyper-fine splitting.
两种手性的 2-溴甲基吡啶 Cu(II) 配合物 [Cu(CHNBr)(NO)]，分别以 2-溴-5-甲基吡啶（L）和 2-溴-4-甲基吡啶（L）为配体，在空气中稳定，以良好的产率生成蓝色材料。晶体结构不同，[Cu(L)(NO)]（）属于单斜晶系 2/c 空间群，而 4-甲基衍生物 则属于三斜晶系 1¯。分子结构中 Br 取代基的取向（() 与 （）构象）以及 Cu(II) 周围的几何形状在整体 4 + 2 扭曲配位中非常不同，在 中，CuNO 基面的每一侧都有两个次要（轴向拉长）Cu-O 键，而在 中，只有一侧有两个。在 中，两个 Br 取代基非常接近 Cu(II) 中心，彼此也非常接近（Br⋯Br~3.7 Å）。尽管存在这些差异，但两种材料的热行为（TG/DTA）非常相似，起始分解温度约为 160°C，最终产物为 CuO。与此相反，两种异构体的 FT-IR 和 Raman 频率明显不同，溶液中的紫外-可见吸收光谱在 263nm（）或 270nm（）处的π-π*吸收和 320nm 左右的配体到金属电荷转移带方面存在显著差异，对于具有更高 Cu(II) 中心对称性的 ，这些差异很明显，但对于 则非常微弱。-依赖性磁化率测量也得到了非常相似的结果（=1.98µ 对于 ，=2.00µ 对于 ，并且 Curie-Weiss 常数非常小，约为-1。两个配合物的 EPR 光谱都表现出轴向对称性，分别具有非常相似的平均 g 值 2.123 和 2.125，以及没有超精细分裂。
